Dispatch group - cannot notify to main thread

Question

After reading Swift 3 evolution on GCD, I am trying to create dispatch group. The problem is the group.notify(queue: do not notify when I pass DispatchQue

Answer 1

After reading post suggested by Matt, I found that I was submitting task to main queue and when I asked to be notified on main thread itself, it got in the deadlock.

I have altered the code and now it is working as intended,

typealias CallBack = (result: [Int]) -> Void
func longCalculations (completion: CallBack) {
  let backgroundQ = DispatchQueue.global(attributes: .qosDefault)
  let group = DispatchGroup()

  var fill:[Int] = []
  for number in 0..<100 {
      group.enter()
      backgroundQ.async(group: group,  execute: {  
          if number > 50 {
            fill.append(number)
          }
          group.leave()

          })
      }

     group.notify(queue: DispatchQueue.main, execute: {
       print("All Done"); completion(result: fill)
     }) 
}

longCalculations(){print($0)}